Can you tell me, what happened prior to this error? Were there any power outages in your area or was the PC properly shut off? I am asking you this, because it seems like there is a corruption of a system register which needs to be repaired.
Do you have a Windows repair or installation CD? If you do, it would be great, because you will need to boot from it. If there is a need to change the boot priority before starting the procedure, please do so. You can do that by entering in the BIOS menu and switching from HDD to DVD/CD /optical device/.
Then, insert the Windows CD and chose the option for the Command prompt. There you must type the following commands followed by the Enter after each of them:
After that, press Enter and wait for your system to be repaired. Please, come and tell me what happened afterwards.